This invention relates generally to the field of high efficiency amplifiers. Certain embodiments of this invention are more particularly related to radio frequency distributed power amplifiers with enhanced efficiency.
In a conventional linear amplifier, DC to AC conversion efficiency is a function of output signal level relative to the DC supply voltage. Conversion efficiency decreases directly as a function of the output level, decreasing as the output signal level decreases. For battery powered devices such as radio frequency transmitters as used in cellular telephones and two-way radios, this limitation in efficiency imposes significant limitations on the battery life that can be expected for the device.
In some instances, the efficiency of a linear amplifier can be enhanced by modulating the supply voltage to the linear amplifier. In this technique, the amplifier""s supply voltage is dynamically modified so that it approximately follows the envelope of the signal driving the linear amplifier. This keeps the supply voltage at or near the output voltage to enhance the amplifier""s efficiency. Unfortunately, this technique cannot be universally applied to all linear amplifiers and generally requires that a DC-to-DC converter circuit be used to provide the supply voltage to the amplifier circuitry.